Solariums and greenhouses are often either too hot during the day or too cold at night. Low emissivity glass helps reduce the cold, but not the hot condition; darkened glass helps reduce the hot, but not the cold condition. Shades installed on the inside of a roof panel or window help reflect the visible light out, but the infrared portion is trapped inside, and further, their thermal insulating value is also marginal.
A more effective way of shading and insulating is to have a retractable reflective shade in between the pair of glazings of the roof window panel. With such an arrangement, excess solar heat is prevented from coming in and the insulating value of the window is improved. The insulating value can be further improved by having multiple shades or sheets within the window to create additional insulating air spaces. Still further improved insulating value can be obtained if the surfaces of the sheets have a low emissivity coefficient, thereby absorbing and reemitting little radiation.
U.S. Pat. No. 4,194,550 (Hopper) discloses an insulating shade apparatus mounted between the pair of glazings of a window. The shade is made of a plurality of sheets which have low emissivity surfaces and which unwind from a retracting spring roller. The sheets are kept spaced apart by various means for creating insulating air spaces. The sheets are pulled down by means of a cable or the like and are retracted by the spring inside the roller. In one embodiment, the window is used at a sloped angle, but, as pointed out, strong spring and cable tension are required to keep the sheets taut in order to keep the sheets in the spaced relation need for maintaining the air spaces between the sheets and the glazings.
Canadian Patent No. 1,174,904 (Dube) and EPO 063 541 A2 (Seska) both disclose a double thickness roller shade made of a single continuous low emissivity sheet which unwinds between a pair of glazings. The sheet unwinds from a driven shade roller; and the opposite end of the sheet is fastened at the upper end of the window frame. The weight of a tensioning roller resting freely on the sheet keeps the sheet tensioned downward in a U-shaped configuration. In combination with the pair of glazings the sheet thus defines three insulating air spaces. This arrangement is attractive for its simplicity, however, it cannnot be used for windows at a substantially sloped angle since the weight of the tensioning roller will not hold the sheet taut enough to prevent excessive sagging of the sheet and maintain the air spaces.
U.S. Pat. No. 2,349,368 (Myers) discloses a retractable roller type flexible curtain, which is capable of being used at an angle, for controlling the flow of air or gas in a duct. The curtain has a U-shaped configuration when extended, however, the object of the flexible curtain is to control gas flow and there is no attempt to maintain the legs of the U-shaped curtain separated to create air spaces when extended.